1. Field of the Invention
The present invention relates to a sliding component for an internal combustion engine, and specifically to a sliding component formed of titanium or a titanium alloy. The present invention also relates to an internal combustion engine and a transporter including such a sliding component, and a method for producing the sliding component.
2. Description of the Related Art
Recently, titanium alloys have become increasingly used as a material for a component for an internal combustion engine, especially for a component making a reciprocating motion such as a connecting rod, a lifter, a valve or the like, for the purpose of decreasing the weight thereof. Titanium alloys, although being lightweight, have a high activity and thus have a low seizure resistance. Titanium alloys are less hard than steel and thus have a lower abrasion resistance. Therefore, a component formed of a titanium alloy is treated with surface hardening such as, for example, oxidation, nitrification, carbonization or the like. As a result of surface hardening, a surface hardened layer is formed on a surface of the component and thus the seizure resistance and the abrasion resistance are improved.
For using a component formed of a titanium alloy as a sliding component that is slidable while being in contact with another component, it is preferable that the surface of the component has the lowest possible coefficient of friction. For this purpose, it is proposed to form a diamond-like carbon (DLC) layer having a low coefficient of friction on the surface hardened layer. For example, Japanese Laid-Open Patent Publication No. 2006-257942 discloses a technology of treating a surface of a titanium alloy tappet with carburizing as surface hardening to form a carbide layer and then forming a DLC film on the carbide layer (surface hardened layer).
However, formation of a DLC film on the surface hardened layer has the following problem. The surface hardened layer such as a carbide layer, an oxide layer or the like is a ceramic layer, and thus has a low adhesiveness to the DLC film. Therefore, the DLC film is likely to be delaminated when the component receives an impact, and thus has a low impact resistance.
Japanese Laid-Open Patent Publication No. 2006-257942 describes that the adhesiveness of the DLC film to the carbide layer is improved by removing an oxide cover layer formed on a surface of the carbide layer before forming the DLC film. However, the research conducted by the present inventor revealed that a sufficiently high adhesiveness or impact resistance cannot be provided even by the method described in Japanese Laid-Open Patent Publication No. 2006-257942.